The Super-Enrichment Mechanism Of Spersed Elements In Sphalerite In Bainiuchang Silver Polymetallic Deposit In Southeast Yunnan

Bainiuchang silver polymetallic deposit is one of the super large deposits in Southeast Yunnan.Bainiuchang Gejiu and Dulong tin-polymetallic deposits forms the polymetallic metallogenic belt in Southeast Yunnan.The lack of research on spersed elements in Bainiuchang silver polymetallic deposit limits the establishment of the enrichment mechanism of spersed elements in the polymetallic metallogenic belt in Southeast Yunnan.Based on the comprehensive analysis of the existing research results of the deposit,We conducted field investigation and collect ore samples.Combined with the mineralogical,isotopic geochemical,elemental geochemistry,single mineral trace element mapping of typical sphalerite and its associated minerals in the deposit,this paper analyzed and studied the origin,distribution and super-enrichment mechanism of spersed elements in sphalerite.The main results are as follows:1.In of Bainiuchang silver polymetallic deposit is mainly enriched in marmatite in cassiterite bearing ore.The variation range of In content in marmatite is 87.59～3354.49 ppm,which is 1151.8～67089.8 times richer than that in the upper crust（0.05 ppm）.The distribution of In in minerals is positively correlated with Cu.The variation range of Cd content in marmatite is 1102.22～6180.4 ppm,which is11247.14～63065.3 times richer than that in the upper crust（0.098 ppm）.Cd is uniformly distributed in minerals.Ga and Ge are not enriched in the marmatite.2.The Pb isotopic composition of galena associated with sphalerite is as follow:²⁰⁶Pb/²⁰⁴Pb is 18.350～18.396,²⁰⁷Pb/²⁰⁴Pb is 15.678～15.691、²⁰⁸Pb/²⁰⁴Pb is38.846～38.893.The distribution of Pb isotope data is very concentrated,the data are similar to the Pb isotopic data of ore minerals in Bainiuchang,Bozhushan granite feldspar and Bozhushan granite contact zone,and is quite different from that of regional strata.It shows that the regional strata of Bainiuchang mining area have little influence on the source of metallogenic Pb.The Pb in Bainiuchang silver polymetallic deposit may mainly comes from Bozhushan granite.The S isotopes of symbiotic sulfide of sphalerite are mainly distributed in the range of 2.7‰～3.8‰,The distribution of S isotope data is concentrated that shows the characteristics of single magma S source.These S and Pb isotopic characteristics suggest that the spersed elements in sphalerite may come from the Bozhushan granitic magma of late Yanshan Period.3.By comparing the In content of cassiterite,chalcopyrite inclusion in sphalerite,pyrite inclusion in sphalerite and sphalerite where the inclusion is located,it is found that In is easier to enter sphalerite than chalcopyrite and pyrite.LA-ICP-MS point data of sphalerite shows that the content of In in sphalerite is mainly positively correlated with Cu,suggesting that the main substitution mechanism of In in sphalerite is Cu⁺+In³⁺→2Zn²⁺,and a small amount of Ag and Fe ions may also be involved in the substitution.The Mapping image of single mineral shows that chalcopyrite is not rich in In,but it can bring a large amount of Cu ions to sphalerite,making In more enriched near chalcopyrite inclusions in sphalerite.4.LA-ICP-MS point data show that in different ores,sphalerite with less exsolution of chalcopyrite is more enriched than sphalerite with more exsolution of chalcopyrite;In the same kind of ores,sphalerite with less exsolution of chalcopyrite is also more enriched than sphalerite with more exsolution of chalcopyrite.This may be related to the metallogenic environment of sphalerite.The sphalerite metallogenic fluid with more exsolution of chalcopyrite has more Fe³⁺,and the fluid environment is more oxidation,which is not conducive to the enrichment of In.5.The enrichment of Cd in sphalerite is mainly affected by Zn/Cd in the fluid,and the data of Zn/Cd is caused by the different consumption rates of Cd and Zn in the process of hydrothermal migration.The main substitution mechanism of Cd in sphalerite is Cd replaces Zn or Fe in sphalerite.Which it replaces depends on the concentration of Cd in the fluid or the metallogenic temperature of sphalerite.